Effect of Cooperative CSI in Adaptive Subcarrier Allocation for OFCDM Based Decode-and-Forward Relay Systems

In this paper, we first propose a modified adaptive subcarrier allocation algorithm for a two-hop decode-and-forward OFCDM relay system and then its BER performance analysis is formulated and numerically evaluated via Monte-Carlo simulation. The effect of considering the CSI of source-base station and source-relay links are evaluated in a cooperative diversity system. Results show that the allocation of subcarriers based on source-relay link CSI provides better BER performance at higher E_b/N_o and at lower E_b/N_o, both the source-relay and source-base station links need to be considered. We also introduce a parameter called cooperative channel state information, C-CSI-(0 ¿ v ¿ 1), that weighs in end-to-end SINR and hence impacts the subcarrier allocation in OFCDM systems. From our numerical simulation, we notice that the cross-over E_b/N_o point (around which frequency spreading gives better performance than time spreading) moves towards the lower E_b/N_o when v approaches 1; that is, when the subcarrier allocation is done giving more weight to source-base station link rather than the source-relay link. We also observe a relationship between the cross-over point (E_b/N_o in dB) and the C-CSI, which provides additional flexibility in operating environment for OFCDM systems.